A faster but unpleasant method of stopping an addictive habit, such as drugs or alcohol. It means that you just totally, completely stop, and never do it again (or at least try to).
Going cold turkey is opposed to stopping it by gradually doing it less and less, or stopping it with help like special gum or medicine. You don't get any help; you just stop.
Lydia tried to smoke only one cigarette a week, but she ended up going back to her old habits. She decided to try out going cold turkey.
"Cold turkey" is a term describing the actions of a person who gives up his habit or addiction at a single moment, rather than through gradually easing the process through tapering off or supplemental medication. The term allegedly derives from the comparison of a cold turkey carcass and the state of a withdrawing addict -- most notably, the cold sweats and gooseflesh. It is often preceded by the word 'going', as 'going cold turkey'."--Wikipedia
Although that word is based on the movie 'Casablanca', it does not have to be a romantic movie from the 40's. It simply must be considered a 'classic' for its genre, even if it's something like fanfiction where nothing has been around for many years.
"After the End" by Arabella and Zsenya is considered the Casablanca of Harry Potter fanfiction.